Appliance control circuit

ABSTRACT

An appliance control circuit for dryer or a combination washer dryer employs a plurality of thermostat devices and a timer to control the heat supplied to the appliance from a pair of heating elements to provide a modulated heat supply and a cool-down portion for the drying cycle.

United States Patent [72] Inventors Richard L. Garfield;

Harold S. Stacik, St. Joseph, Mich. [211 Appl. No. 803,818

[22] Filed Mar. 3, 1969 [45] Patented Mar. 23, 1971 [73] Assignee Whirlpool Corporation Benton Harbor, Mich.

541 APPLIANCE CONTROL CIRCUIT 10 Claims, 3 Drawing Figs.

[52] US. Cl 34/45, 34/48 [51] Int. Cl. F26b 13/10 [50] Field of Search 34/45, 48

[56] References Cited UNITED STATES PATENTS 3,213,548 10/1965 Deaton 3,216,126 1 1/ 1965 Brucken et al 34/45 3,218,730 11/1965 Menk et a1 34/48X 3,318,016 5/1967 Chafee 34/48X 3,391,467 7/1968 Miller et a1. 34/45 3,397,461 8/1968 Fogt et al 34/45 3,398,462 8/1968 Harter 34/45 Pn'mkzry Examiner-Carroll B. Dority, Jr.

Att0rneys-Thomas E. Turcotte, James S. Nettleton, Donald W. Thomas, Burton H. Baker, Franklin C. Harter, Gene A. Heth and Hill, Sherman, Meroni, Gross and Simpson ABSTRACT: An appliance control circuit for a dryer or a o b nat n a h r. Q ys yia r al tx thermostat devices and a timer to control the heat supplied to tlie appliance from a pair of heating elements to provide a modu lated heat supply and a cool-down portion for the drying cycle.

APPLIANCE CONTROL CIRCUIT This invention relates to domestic appliances and particularly to dryers or combination washer dryers, and more particularly to a dryer apparatus having a control circuit for controlling the application of heat of the dryer drum in response to the heat of the exhaust air and the operational sequence of tinting apparatus.

2. Description of the Prior Art It is generally known in the art to provide a dryer including a control circuit having a pair of heaters connected in parallel to an energizing circuit wherein the energizing circuit for one of the heaters is controlled by a thermostat, which also controls the operation of a time delaythermostat. When the controlled heater has been deenergized for a predetermined period the time delay thennostat opens terminating the cycle. It is also known in the art to provide a dryer with a control circuit in which a timer and a pair of heaters are initially energized, and wherein, after a short interval the timer is deenergized and placed under the control of a normally open thermostat contact. Energization of the thermostat in response-to a rise in temperature in the dryer effects deenergization of heaters and a second .energization of the timer. The timer operates for a brief period and,after such period, permanently opens the energizing circuit to one of the heaters and places the other heater and the timer under the control of the thermostatwith this configuration, drying continues with heat being supplied by one heater until the trip point for the thermostat is reached a second time causing deenergization of the heater and energizaton of the timer. Shortly after energization of the timer, the powering circuit to the heaters isdeenergized and a circuit to the timer independent of the thermostat is established to a provide a cool-down portion for the drying cycle.

SUMMARY OF THE INVENTION According to the present invention, an appliance dryer is provided with a pair of heating elements in which one of the heating elements is controlled by a thermostat to provide a modulated heat input for the dryer, and in which the timer motor may be under the control of a normally open contact of the thermostat which controls the one heating element to obtain intermittent operating power for the timer motor. Further, a timer contact is provided in the circuit between the normally open then'nostat contact and the timer motor to ensure that the other heat element cannot be inadvertently energized by way of the thermostat during the terminal portion of the drying cycle.

Briefly, a dryer constructed in accordance with the present invention is advantageously provided with a combination ofan automatically controlled drying cycle with a modulated heat supply and will advantageously produce better results than a timed control circuit at a lower cost than is provided by an electronic control system.

BRIEF DESCRIPTION OF THE DRAWINGS tion of the plurality of contacts of the timer employed in FIGS. 7

1and2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings'a clothes dryer is illustrated generally at l including a frame 2 which defines a housing for a drying drum 7, a heater box 4 having an air inlet 5 and an input manifold 6 in communication with the drum 7, an inlet 8 of an exhaust v duct 9, in communication with the drum 7 and a discharge outlet 11. A lint screen or filter I0 is provided at the input 8 of exhaust duct 9. Also housed within the frame 2 is a motor 35, a belt coupling the motor,35 to the drum 7 in a driving relationship, a pair of heat responsive thermostat devices 54 and 59, and a pair of heating elements 64 and 65, which are typi-' cally 4l00 and 1500 watts, respectively.

A timer 42 and other control switches, such as a push-tostart switch 31 are housed in console 3 which is carried on the upper surface of the frame 2. A fan (not shown) is linked to and operated by the motor 35 during drying to establish the air flow shown by the curved arrows to provide fresh air at input 5 of heater box 4 and at exhaust outlet for the air flow.

The dryer is connected to a power supply, for example a three-wire 230 volt commercial supply, at terminals LI, L2 and N. With such a commercial supply, a 230 volt potential is provided across terminals Ll-L2 and H5 volt potential'is provided across terminals Ll-N and also across terminals L2-N. With these potentials applied to the aforementioned terminals the control circuit, generally referenced 20, may be operated. It can be seen from FIG. 2 that the control circuit 20 is divided such that one portion of its components is generally associated with '1 l5 volt operation from terminals Ll--N and another portion of its components are generally associated with 230 volt operation provided by way of terminals LI-LZ.

The control circuit 20 comprises a door-operated switch 21 generally connected between terminals L1 and N and a lamp 27 also generally connected between terminals LI and N. One of the primary functions of the door switch 21 is to prevent operation of the dryer with the door in open position. Lamp 27 indicates that the door is not in the closed position; it also is employed to indicate that drying cycle is in progress. This cir' cuit also comprises a push-to-start switch 31, a motor 35 for rotating drum 7 and for operating the aforementioned fan, and

a timer 42 for partially establishing and controlling the plurali-v ty of drying cycles. A pair of thermostats 54 and 59, a pair of heating elements 64 and 65, and a centrifugally-operated switch 66 are connected between terminals Ll andLZ for completing the 230 volt circuit.

More specifically, the control circuit 20 comprises a dooroperated switch 21 including movable contacts 22 and 25 and stationary contacts 23, 24 and 26 connected between ter minals L1 and N. Lamp 27 is connected between the movable terminal 22 of switch 21 and the terminal N. A timer 42 is con: nectable to terminal N by way of contacts 25 and 26 of switch 21. On the other hand, contacts of timer 42 are connected to terminal Ll. Timer .42 comprises a timer motor 43 and a plurality of movable contacts 44, 46, 48, 50 and 52 and their associated fixed contacts 45, 47, 49, 51, and 53. The initial and operational conditions of these contacts can be seen by referring to the timer schedule of FIG. 3 wherein the crosshatched bars represent contact closure and the open bars represent open conditions of contacts.

Control circuit 20 also comprises motor 35 which is employed to rotatably drive the drum 7 'by way of the belt 12. Motor 35 is also connected on one side to the terminal N by way of contacts 25 and 26 of switch 21 and conductor 36 and comprises a starting winding 37, a running winding 38, a centrifugally operated movable contact 39, a fixed contact 40 and another fixed contact 41. Contact 39 is illustrated in the starting position wherein it is closed to contact 40. Motor 35 is connectable to terminal Ll by way of contact 44-45 and 46- 47 of timer 42 by way of contacts 29-30 of relay 28. For starting purposes, relay 28 is initially unoperated and contacts 29 and 30 are opened; therefore, a push-to-start switch 31 is 5 included in the motor starting circuit. Push-to-start switch 31 includes a spring loaded movable contact 32 and a pair of fixed contacts 33-34 which are connected in shunt relation to contacts 29-30 of relay 28.

The control circuit also comprises a safety thermostat 54 which is disposed on the heater box 4 adjacent the heating elements 64 and 65. Thermostat 54 therefore senses the heat being supplied by heaters 64 and 65 to the air flowing toward the drum 7. Thermostat 54 includes a heat sensitive element 55 having a movable contact portion 56 which is normally closed to a contact 57 and which is movable to close with contact 58. Thermostat 54 is connectable to tenninal L1 by way of timer contacts 52-53. Connected to tenninal 57 of thermostat 54 is a second thermostat 59 which is disposed near the exhaust end of exhaust duct 9 to sense the heat of the air flowing from drum 7. Thermostat 59 includes a heat sensitive element 60 having a movable contact 61 normally closed to contact 62 and movable to close with contact 63. The nonnally closed contact 57 and 62 of thermostats 54 and 59, are connected to heating elements 65 and 64 respectively. The heat sensitive element 60 of thermostat 59 is also connected to heating element 65. The normally closed contact 57 of the thermostat 54 is connected to heating element 64 through thermostat 59. The normally open contacts 58 and 63 of thermostats 54 and 59, respectively, are commonly connected to fixed contact 51 of timer 42. Contacts 50-51 of timer 42, it should be noted, are closed only during the AUTOMATIC drying cycle and therefore permit thermostatic control of the timer 42 during the automatic cycle.

To operate in the TlMED drying cycle, the door is opened placing contacts 22 and 24 in a closed condition to light lamp 27 and placing contacts 25 and 26 in an opened condition to prevent operation of the dryer. Wet laundry is positioned within the drum 7 and the door is closed to open contacts 22 and 24, lamp 27 thereby being extinguished, and to close contacts 25 and 26 to prepare a powering circuit for the motor 35 and the timer motor 43 over conductor 36. Push-to-start switch 31 is momentarily depressed to extend a powering circuit from terminal L1 to the motor 35 over the circuit including contacts 44-45, 33-32-34, 46-47 to the running winding 38 of motor 35, and additionally over contacts 39- 40 to the starting winding 37 of motor 35. Motor 35 therefore starts and upon reaching a predetermined speed, switch contact 39 is centrifugally operated away from contact 40 and the motor operation is sustained over running winding 38.

The momentary closure of contacts 33-32-34 also provides lighting power to lamp 27 by way of contacts 22-23, to indicate that a drying cycle is in progress and also completes an operating circuit for relay 28, the operating circuit being previously partially established by way of door switch contacts 25-26. Lamp 27 therefore lights and relay 28 operates to close contacts 29-30 for sustaining operation of the motor and illumination of the lamp 27 upon release of the push-tostart switch 31.

Contacts 48-49 of timer 42 also extend power from the above traced path to timer motor 43 which operates for a predetermined interval at which time contacts 44-45, 46- -47 and 48-49 are opened to, in turn, open the above traced powering paths from terminal L1 and inhibit operation of lamp 27, relay 28, motor 35 and timer motor 43. In the interim, however, timer contacts 52-53 are closed completing a circuit to one side of the 230 volt thermostat and heating element circuitry. This circuit was previously partially established by centrifugal switch 66 which, upon sufiicient speed of drum 7, closed contact 67 to contact 68. The thermostat 54 therefore controls the application of power to the heating elements 64 and 65 in response to the heat being delivered by said elements to the air flow into the drum. Thermostat 59 additionally controls the application of heat from element 64 to the air flow in response to the heat of the air flowing out of the drum 7 through the exhaust duct 9.

After a predetermined heating interval contacts 52-53 are opened by timer motor 43 prior to the opening of contacts 44- -45, 46-47 and 48-49 so that the heating elements 64 and 65 no longer receive heating current and the dryer motor 35 and the fan continue to run for a short cool-down period during the latter part of the TlMED drying cycle.

lt is evident from the timer schedule of FIG. 3 that the timer may be set to an AIR drying cycle wherein timer 42 does not operated the contacts 52-53 to a closed condition. The MR drying cycle is therefore very similar to the TIMED drying cycle, except for the application of the heat.

In operation of the AUTOMATlC drying cycle, the wet laundry is loaded as hereinabove described, the door is closed. and the timer is set for automatic operation wherein contacts 44-45, 46-47, 50-51 and 52-53 are initially closed. The push-to-start switch 31 is operated to start the motor 35, and upon closure of switch 66 by centrifugal force, heaters 64 and 65 are energized. It should be noted that the timer motor 43 is not operating at this time in that contacts 48-49 are open.

As the laundry begins to dry, the exhaust temperature begins to rise, and at a predeten'nined temperature, the exhaust thermostat 59 transfers the contact element 61 away from element 62 to contact 63 to complete a power circuit to the timer motor 43 over the path including terminal L1, closed timer contacts 52-53, heat responsive element 55 and its contact 56, contact 57, heat responsive element 60 and its contact 61, contact 63 and closed timer contacts 50-51. The other side of the timer motor is connected to terminal N by way of contacts 25-26 of the door switch. Therefore, when the temperature of the exhaust air rises to a predetennined level, operation of the timer motor is initiated under the control of the exhaust thermostat 59.

The exhaust thermostat 59 will open and close contact 6] between contacts 62 and 63 a number of times determined by the amount of moisture contained in the load dried to provide a modulated heat input to drum 7. After a sufficient time has accumulated, the timer motor 43 advances to the point at which contacts 48-49 close to provide a circuit to the timer motor which is independent of the exhaust thermostat 59. This circuit includes tenninal Ll, closed timer contacts 44-45, closed relay contacts 29-30, closed timer contacts 46-47 and closed timer contacts 48-49. The timer motor therefore continues to advance for a certain interval upon which timer contacts 52-53 are operated to an open condition, thus removing the energizing power from the heaters 64 and 65. The powering circuit to the motor 35 remains unaffected at this time and the motor continues to -run providing a cooldown portion for the cycle. To prevent energizaton of heater element 65 during this portion of the cycle through the exhaust thermostat 59, timer contacts 50-51 are operated to open and remove the possibility of a powering path through the timer contacts and the exhaust thermostat.

Although minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.

The embodiments of the invention in which an exclusive property of privilege is claimed are defined as follows.

We claim:

1. In combination with drying apparatus of the type including a treatment zone through which a stream of temperature conditioned air is directed by air translation means, the improvement of a control circuit comprising:

a driving motor means and a presettable timing device in said circuit to control the operation of the apparatus in a preset program;

means for conditioning the temperature of the air stream;

modulating means for modulating the operation of said temperature conditioning means; and

switching means for controlling the operation of said motor means and said modulating means during a drying cycle including manually positionable means for said timing device to select a plurality of timed intervals within a drying cycle and a plurality of contacts coupled to said timing device and selectively operable thereby upon the timing of said intervals, said plurality of contacts including,

a first set of normally closed contacts connected between said motor and the power supply, said first set of contacts being opened upon the occurrence of a third interval to terminate operation of the drying apparatus,

a second set of normally closed contacts connected between said modulating means and the power supply,

said second set of contacts being operable to prohibit energization of said temperature conditioning means upon the occurrence of a second of said intervals,

a third set of normally closed contacts connected between said modulating means-and said timing device to permit intermittent powering of said timing device via said modulating means during a first of said intervals, said third set of contacts being open during a second of said intervals, and

a fourth set of normally open contacts connected between ,said first set of contacts and said timing "device, said fourth set of contacts being closed upon completion of the timing of the first interval to effect a steady energization of said timing device.

. 2. The laundry drying apparatus defined in claim 1, wherein said modulating means includes a thermostat device disposed for sensing the temperature of the air directed out of said treatment zone and includingcontacts which are operable to selectively modulate said temperature conditioning means in accordance with the air temperature sensed thereby.

3. The laundry drying apparatus defined in claim 1, wherein said modulating means comprises a thermostat including a heat sensitive element having a transfer contact, a contact normally closed to said transfer contact connected to said temperature conditioning means, and a contact normally open from said transfer contact connectedto said third set of contacts, said thermostat being disposed adjacent air directed out of said treatment zone and operable in response to the temperature sensed by said heat sensitive element to provide energizing power alternately to said temperature conditioning means and said timing device.

4. Laundry drying apparatus comprising in combination: a

' rotatable hollow receptacle for receiving a supply of materials to be dried; a motor coupled to and operable to rotate said receptacle for turnblinglaundry therein; means in communication with the interior of said receptacle for providing a flow I of heated air therethrough including fan means connected to and driven by said motorto establish said air flow, and means for heating the flowing air including. first andsecond heater elements; and a control circuit for controlling the operation of said motor andsaid heating means, said control circuit including input terminals for connection to a power supply, modulating means connected in circuit with said input tenninals and said heating means and operabletd intermittently connect said first and second heater elements in parallel for intermittent energizaton of said first heater element, and timing means connected to said input terminals, to said motor and to said modulating means, said timing means including a manually adjustable timer for establishing a powering circuit for said motor for a timed interval including first contacts interposed between said input terminals and 'said motor, said timing means being connected to and intennittently operated by said modulating means alternately-with said first heater'element over a first portion of said interval, second contacts interposed between said timer and said input terminals for establishing a powering circuit for said timer for a second portion of said'interval, and third contacts vconnected in circuit with said heating means and said input terminals for establishing a powering circuit for said heating means for a period less than said timed interval during which period said second heater element is continuously energized.

5. A control circuit for controlling the operation of a laundrydryer of the type having'a rotatable receptacle for holding and tumbling laundry, motor means for rotating the receptacle and means for providing a flow of air through the receptacle, said control circuit comprising:

a power input for connection to a source of electrical ener- By timing means including an electrically operated timing device which is manually positionable to select an auto matic drying cycle, and a plurality of contacts coupled to said device and operated thereby at timed intervals within the automatic drying cycle;

heating means for heating the air flow connected to said power input by a first set of said plurality of contacts which are normally closed upon selection of said automatic drying cycle and opened by said timing device at a second of said timed intervals; I

modulating means in circuit connected with said first set of contacts and with said heating means and said power input, said modulating means including a heat sensitive element disposed in the air flow tosense the temperature thereof and modulate the energiration of said heating means in accordance therewith;

a second set of said plurality of contacts being normally closed upon selection of saidautomatic drying cycle and connecting said modulating means to said timing device, said second set of contacts providing intermittent energization of said timing device by said modulating means. and said second set of contacts being opened by said timing device at the second of said timing intervals;

a third of said plurality of contacts being normally closed upon selection of said automaticdrying cycle and connected between said power input and the motor means of the dryer, said third set of contacts being operated to an open condition by said timing device at a third interval of said drying cycle; and

a fourth set of said plurality of contacts being normally open upon selection of said automatic drying cycle and connected between said timing device and said third set of normally closed contacts, said fourth set of contacts being closed by said timing device upon accumulation during the first interval by intennittent energization to provide continuous energization of said timing device and opened at a fourth interval to inhibit energization of said timing device. v

6. Thecontrol circuit set forth in'.c-laim 5, comprising centrifugally operated switch means coupled to the motor means and connected between said heatingmeans and said power input for preventing energization'of said heating means until the receptacle is rotated at a predetermined speed.

7. The control circuit set forth in claim 5. comprising a door-operated switch including contacts interposed between said relay contacts and between said relay winding and said power input, the manual operation of said switch energizing said relay to complete the powering circuit to the motor means through said third set of contacts.

9. The control circuit set forth in claim 5, wherein said heating means includes first and second heater elements connected in parallel relative to said power input and said modulating means is connected in series with said first heater element. i,

10. The control circuit set forth in' claim 9. wherein said modulating means comprises a thermostat including a heat sensitive element having a transfer contact, a contact normally closed to said transfer contact connected to said first heater element, and a contact normally open from said transfer contact connected to said second set of contacts.

Patent No. 3,571,941 Dated bAarch 23, 1971 Inventor(s) Richard L. Garfield and Harold S. Stacik It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, line 10, delete "and";

line 19, read "motor" as motor means Claim 5, line 18 should read modulating means connected in circuit with said first set of Signed and sealed this 6th day of July 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER Attesting Officer Commissioner of Pat 

1. In combination with drying apparatus of the type including a treatment zone through which a stream of temperature conditioned air is directed by air translation means, the improvement of a control circuit comprising: a driving motor means and a presettable timing device in said circuit to control the operation of the apparatus in a preset program; means for conditioning the temperature of the air stream; modulating means for modulating the operation of said temperature conditioning means; and switching means for controlling the operation of said motor means and said modulating means during a drying cycle including manually positionable means for said timing device to select a plurality of timed intervals within a drying cycle and a plurality of contacts coupled to said timing device and selectively operable thereby upon the timing of said intervals, said plurality of contacts including; a first set of normally closed contacts connected between said motor and the power supply, said first set of contacts being opened upon the occurrence of a third interval to terminate operation of the drying apparatus, a second set of normally closed contacts connected between said modulating means and the power supply, said second set of contacts being operable to prohibit energization of said temperature conditioning means upon the occurrence of a second of said intervals, a third set of normally closed contacts connected between said modulating means and said timing device to permit intermittent powering of said timing device via said modulating means during a first of said intervals, said third set of contacts being open during a second of said intervals, and a fourth set of normally open contacts connected between said first set of contacts and said timing device, said fourth set of contacts being closed upon completion of the timing of the first interval to effect a steady energization of said timing device.
 2. The laundry drying apparatus defined in claim 1, wherein said modulating means includes a thermostat device disposed for sensing the temperature of the air directed out of said treatment zone and including contacts which are operable to selectively modulate said temperature conditioning means in accordance with the air temperature sensed thereby.
 3. The laundry drying apparatus defined in claim 1, wherein said modulating means comprises a thermostat including a heat sensitive element having a transfer contact, a contact normally closed to said transfer contact connected to said temperature conditioning means, and a contact normally open from said transfer contact connected to said third set of contacts, said thermostat being disposed adjacent air directed out of said treatment zone and operable in response to the temperature sensed by said heat sensitive element to provide energizing power alternately to said temperature conditioning means and said timing device.
 4. Laundry drying apparatus comprising in combination: a rotatable hollow receptacle for receiving a supply of materials to be dried; a motor coupled to and operable to rotate said receptacle for tumbling laundry therein; means in communication with the interior of said receptacle for providing a flow of heated air therethrough including fan means connected to and driven by said motor to establish said air flow, and means for heating the flowing air including first and second heater elements; and a control circuit for controlling the operation of said motor and said heating means, said control circuit including input terminals for connection to a power supply, modulating means connected in circuit with said input terminals and said heating means and operable to intermittently connect said first and second heater elements in parallel for intermittent energizaton of said first heater element, and timing means connected to said input terminals, to said motor and to said modulating means, said timing means including a manually adjustable timer for establishing a powering circuit for said motor for a timed interval including first contacts interposed between said input terminals and said motor, said timing means being connected to and intermittently operated by said modulating means alternately with said first heater element over a first portion of said interval, second contacts interposed between said timer and said input terminals for establishing a powering circuit for said timer for a second portion of said interval, and third contacts connected in circuit with said heating means and said input terminals for establishing a powering circuit for said heating means for a period less than said timed interval during which period said second heater element is continuously energized.
 5. A control circuit for controlling the operation of a laundry dryer of the type having a rotatable receptacle for holding and tumbling laundry, motor means for rotating the receptacle and means for providing a flow of air through the receptacle, said control circuit comprising: a power input for connection to a source of electrical energy; timing means including an electrically operated timing device which is manually positionable to select an automatic drying cycle, and a plurality of contacts coupled to said device and operated thereby at timed intervals within the automatic drying cycle; heating means for heating the air flow connected to said power input by a first set of said plurality of contacts which are normally closed upon selection of said automatic drying cycle and opened by said timing device at a second of said timed intervals; modulating means in circuit connected with said first set of contacts and with said heating means and said power input, said modulating means including a heat sensitive element disposed in the air flow to sense the temperature thereof and modulate the energization of said heating means in accordance therewith; a second set of said plurality of contacts being normally closed upon selection of said automatic drying cycle and connecting said modulating means to said timing device, said second set of contacts providing intermittent energization of said timing device by said modulating means, and said second set of contacts being opened by said timing device at the second of said timing intervals; a third of said plurality of contacts being normally closed upon selection of said automatic drying cycle and connected between said power input and the motor means of the dryer, said third set of contacts being operated to an open condition by said timing device at a third interval of said drying cycle; and a fourth set of said plurality of contacts being normally open upon selection of said automatic drying cycle and connected between said timing device and said third set of normally closed contacts, said fourth set of contacts being closed by said timing device upon accumulation during the first interval by intermittent energization to provide continuous energization of said timing device and opened at a fourth interval to inhibit energization of said timing device.
 6. The control circuit set forth in claim 5, comprising centrifugally operated switch means coupled to the motor means and connected between said heating means and said power input for preventing energization Of said heating means until the receptacle is rotated at a predetermined speed.
 7. The control circuit set forth in claim 5, comprising a door-operated switch including contacts interposed between said power input and the motor and said timing device and operable to prepare a powering path for the motor and said timing device upon closure of a door controlling an opening through which the receptacle is charged and emptied.
 8. The control circuit set forth in claim 5, comprising a relay including a winding and normally open contacts serially connected in circuit with said third set of contacts, and a manually operable switch having contacts connected in shunt relation to said relay contacts and between said relay winding and said power input, the manual operation of said switch energizing said relay to complete the powering circuit to the motor means through said third set of contacts.
 9. The control circuit set forth in claim 5, wherein said heating means includes first and second heater elements connected in parallel relative to said power input and said modulating means is connected in series with said first heater element.
 10. The control circuit set forth in claim 9, wherein said modulating means comprises a thermostat including a heat sensitive element having a transfer contact, a contact normally closed to said transfer contact connected to said first heater element, and a contact normally open from said transfer contact connected to said second set of contacts. 